Silver halide emulsions stabilized with manganous salts

ABSTRACT

PROCESS FOR PRECIPITATING SILVER HALIDE GRAINS IN THE PRESENCE OF A THODIUM SALT AND STABILIZING EMULSIONS COMPRISING SAID GRAINS WITH (1) A WATER SOLUBLE MANGANOUS SALT OR (2) A COMBINATION OF SAID WATER SOLUBLE MANGANOUS SALT AND CADMIUM BROMIDE ARE DISCLOSED. PHOTOGRAPHIC EMULSIONS AND ELEMENTS CONTAINING THESE SILVER HALIDE GRAINS ARE ECOLOGICALLY DESIRED AND ARE PARTICULARLY USEFUL IN PROVIDING UNEXPECTED AND IMPROVED SENSITOMERIC PROPERTIES, PARTICULARLY UPON STORAGE.

3,720,516 SILVER HALIDE EMULSIONS STABILIZED WITH MANGANOUS SALTS Robert Newell Woodward and Nelson Robert Sidebotham,

Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N .Y. No Drawing. Filed Oct. 15, 1971, Ser. No. 189,745 Int. Cl. G03c 1/30 U.S. Cl. 96--110 11 Claims ABSTRACT OF THE DISCLOSURE Processes for precipitating silver halide grains in the presence of a rhodium salt and stabilizing emulsions comprising said grains with (1) a water soluble manganous salt or (2) a combination of said water soluble manganous salt and cadmium bromide are disclosed.

Photographic emulsions and elements containing these silver halide grains are ecologically desirable and are particularly useful in providing unexpected and improved sensitometrie properties, particularly upon storage.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to photographic materials, their preparation and use. In one aspect, this invention relates to an improved process for preparing silver halide emulsions by precipitating silver halide grains in the presence of a rhodium salt and stabilizing the emulsions with manganous salts alone or a combination of manganous salts with cadmium bromide. In another aspect of this invention, there is disclosed silver halide emulsions and photographic elements containing these emulsions which are prepared and stabilized according to a process which, in comparison to similar prior art processing offers an ecological advantage.

Description of the prior art When silver halide emulsions are prepared by the precipitation of silver halide grains in the presence of small quantities of a rhodium salt, it is known that the contrast achieved is considerably higher than is obtained with emulsions precipitated in the absence of a rhodium salt. Significant stabilization of silver halide emulsions so prepared -was achieved as described in US. Pat. 3,488,709 issued J an. 6, 1970 to Sidebotham.

Sidebotham employed cadmium bromide as his stabilizing agent with good results and also achieved higher contrast than could have been effected from the rhodium saltcadmium bromide combination. Such results were demonstrated to be unique with respect to cadmium bromide since other closely related compounds, for example, potassium bromide and cadmium chloride failed to impart the same beneficial and desirable properties to silver halide emulsions in which the silver halide grains are precipitated in the presence of a rhodium salt.

The use of the rhodium salts to increase the contrast of the silver halide emulsions is well known and taught in British Pat. 775,197 and Glafkides Photographic Chemistry, volume I (1958), page 351 as well as in US. Pat. 3,488,709 issued Jan. 6, 1970 to Sidebotham.

Unfortunately, and even though the concentrations of cadmium bromide taught in US. Pat. 3,488,709 are relatively small, i.e. 20 to about 60 grams per mole of silver halide, the elimination or reduction of such cadmium salts now appears to be ecologically advantageous since, during film processing, such cadmium salts are eventually washed out and find their way into the environment. Thus, it is known that cadmium interferes with zinc and nited States Patent Ofifice 3,720,516 Patented Mar. 13, 1973 copper metabolism and is harmful to living organisms. Cadmium can be found not only in the atmosphere but also in marine life, such as in fish found in waters wherein cadmium is present in high levels.

In view of the now recognized toxicity of cadmium and other trace metals, applicants concern for the public health and the maintenance of a more normal ecological balance has led to new means of achieving good sensitometric results in photographic compositions by utilizing substantially less toxic or non-toxic metals wherever possible.

The improved photographic compositions described herein, although they contain reduced levels of cadmium or none at all, unexpectedly exhibit significant emulsion stability and even show a slight speed increase. This reduction or elimination of the cadmium pollutant has been achieved by substituting, in whole or in part, relatively harmless water soluble manganous salts for cadmium salts in photographic silver halide emulsions containing silver halide grains precipitated in the presence of rhodiurn salts.

SUMMARY OF THE INVENTION In accordance with this invention there is provided photographic silver halide emulsions and elements which provide improved and unexpected sensitometric results with the elimination or substantial reduction of harmful environmental pollutants. In particular, the desirable photographic results of stabilization against speed loss, particularly on storage, are achieved by total or partial replacement by the relatively harmless trace metal manganous salts by cadmium salts in photographic materials containing silver halide grains which are precipitated in the presence of rhodium salts.

It is an object of this invention to provide new and improved processes for preparing high speed, stabilized silver halide grains precipitated in the presence of a rhodium salt.

It is another object of this invention to provide improved emulsions and elements containing said emulsions, whereby significant and desirable speed stabilizing effects on storage and under adverse keeping conditions are achieved by the use of relatively harmless trace metal salts.

It is yet another object of this invention to provide unexpected and improved stabilizing activity in high speed light sensitive compositions containing silver halide grains prepared and precipitated in the presence of rhodium salts.

Other objects of this invention will become obvious to those skilled in the art from the specification and examples which follow.

DESCRIPTION OF PREFERRED EMBODIMENTS In accordance with this invention, the above and other objects are attained with novel and improved high speed silver halide materials containing at least some manganous salts as a stabilizer alone or in combination with varying amounts of cadmium bromide. These materials include silver halide emulsions prepared by precipitating silver halide grains in the presence of a rhodium salt.

In one embodiment, this invention relates to a process for preparing a photosensitive silver halide emulsion which process comprises precipitating the silver halide grains of said emulsion in the presence of a rhodium salt and adding to said emulsion, a stabilizing concentration of (l) a water soluble manganous salt or (2) a combination of said salt with cadmium bromide.

A particularly useful concentration of manganous salts is about 3 grams to about 50 grams per mloe of silver where only the water soluble manganese salts are employed for stabilization. Where used in combination with cadmium bromide, i.e. as a partial replacement therefor,

manganous salts are present in a range of from about weight percent to about 90 weight percent of the combination of these speed stabilizing agents. When used in such combinations, cadmium can be present in a concentration of from about 5 to about grams per mole of silver and manganous salts are present at about 5 to about 50 grams per mole of silver.

These stabilizing agents can be added to the emulsion after the formation of the silver halide grains in the presence of rhodium salts. It has been unexpectedly found that according to this invention even Where cadmium salts, such as cadmium bromide, are used in combination with manganous salts, effective stabilizing concentrations of cadmium are far below that required when only cadmium salts are used. For example, only about 15 percent to about percent by weight of cadmium bromide is needed in combination with water soluble manganous salts as compared to cadmium when used alone.

In a preferred embodiment of this invention the silver halide grains are precipitated in the presence of a rhodium salt and an organic thioether. Typical of the thioethers found useful in the practice of this invention are those thioether silver halide solvents described in U.S. Pat. 3,371,157 issued Sept. 6, -1966 to McBride. A preferred organic thioether is 1,8-dihydroxy-3,6-dithiaoctane. It has been found that said thioether-s can be used with great advantage in a concentration of from about 0.1 to about grams per mole of silver halide. The rhodium salts are particularly useful in a concentration of from about 0.01 to about 0.25 mg. of rhodium salt per mole of silver formed.

The rhodium salt suitable for the present invention can be any water-soluble rhodium salt useful for the intended purpose and includes those disclosed in the U.S. patents discussed hereinbefore and are employed in the same manner. Typical useful rhodium salts are, for example, rhodium chloride, rhodium trichloride, rhodium ammonium chloride, etc. The rhodium salts can be employed in any concentration which is effective for the intended purposed. Especially good results were found when the concentration is from about 0.01 to about 0.25 milligram per mole of silver halide.

Suitable water soluble manganous salts which are a source of manganous ions in the practice of this invention include the various water soluble inorganic manganous salts such as the chlorides, bromides, nitrates, sulfates and the like. Such salts can be hydrated, as is well known in the art and exemplified by MnCl 4H O, MnSO -H O and the like. In describing the manganous salts found useful in the practice of this invention, it will be understood that these water soluble, usually colorless or sometimes slightly pink inorganic acid salts are preferably derived from the strong acids such as hydrochloric, sulfuric, fiuoric, and nitric acids and the like. However, also included are those salts of other acids such as cabocyclic, benzoic, boric, butyric, cyanic, lactic, acetic and the like wherein manganese has a valence of plus two. While U.S. Pats. 1,976,302 issued on Oct. 9, 1934 to Sheppard et al.; 1,955,- 444 issued on Mar. 26, 1935 to Ilford; 2,839,405 issued on June 17, 1958 to Jones; and 3.556,797 issued on Jan. 19, 1971 to Pattijn et al., all disclose the use of manganese compounds in silver halide emulsions; none of these emulsions contains silver halide grains precipitated in the presence of rhodium salts. Further, as will be seen hereafter, the reduction or complete elimination of significant concentration of cadmium bromide and substitution therefor of manganous salts to affect emulsion stabilization is totally unobvious and unexpected.

In a further preferred embodiment of this invention, there is provided a high speed, high contrast photosensitive silver halide emulsion such as a silver chlorobromide emulsion which is prepared according to the processes described hereinabove. These emulsions are stabilized against speed loss, particularly upon storage for prol g d p iods of tim y st biliz g once tration of (1) a water soluble manganous salt or (2) a combination of said salt with cadmium bromide. Silver halide grains precipitated in the presence of a rhodium salt which are used in such emulsions can be thioether ripened such as with an organic thioether as in McBride U.S. Pat. 3,271,157 described hereinabove. Emulsions of this invention can contain a stabilizing concentration of a combination of a water soluble manganous salt and cadmium bromide wherein the manganous salt is present in about 15 weight percent to about weight percent. Where the water soluble manganous salt is used alone as a complete replacement of the cadmium salt, it is present in a stabilizing concentration of about 3 grams to about 50 grams per mole of silver.

It will be understood that high speed and high contrast are terms well known in the art to refer respectively to photo-sensitive emulsions which require minimal light exposure to record a latent image and are best exemplified by the bromide and the bromoiodide emulsions. These emulsions generally comprise large, coarse grains having a grain size of from .5 m to about 1.5 mg.

As will be seen hereafter the elements of this invention comprise a variety of supports bearing the emulsions described. A preferred support is an alpha-olefin polymer coated paper, that is one coated with a polymer of an aolefin of 2 to 10 carbon atoms, such as polyethylene. This coating can be on one or both sides of the paper.

The general methods for preparing the silver halide emulsions described herein are well known in the art as shown, for example, by the Glafkides reference mentioned hereinbefore. In the improved process of his invention, any technique for making silver halide emulsions can be employed and these include the double-jet technique where solutions of potassium halide and silver nitrate are added to an aqueous gelatin solution already containing potassium bromide.

The silver halide grains employed in this invention are chemically sensitized by any means suitable for this purpose, many methods having been previously described in the prior art. Chemical sensitization, as used herein, includes sensitization of the type described Antoine Hautot and Henri Saubenier in Science et Industries Photographiques," vol. XXVIII, January 1957, pages 1-23 and January 1957, pages 5756. Such chemical sensitization includes three major classes, viz, gold or noble metal sensitization, sulfur sensitization, such as by a labile sulfur compound, and reduction sensitization, i.e., treatment of the silver halide with a strong reducing agent which does not fog appreciably the silver halide but introduces small specks of metallic silver into the silver halide crystal or grain.

The silver halide grains can likewise be chemically sensitized by any of the accepted procedures. Emulsions containing such grains can be digested with naturally active gelatin, or compounds of the sulfur group can be added, such as those described in Sheppard U.S. Pat. 1,574,944 issued Mar. 2, 1926; Sheppard et al. U.S. Pat. 1,623,499 issued Apr. 5, 1927; and Sheppard et al. U.S. Pat. 2,410,- 689 issued Nov. 5, 1946. Particularly good results are obtained with sulfur, selenium, tellurium sensitizers and the like.

The rhodium treated silver halide grains can also be treated with other salts of the noble metals, such as ruthenium, palladium iridium, and platinum. Representative compounds are ammonium chloropalladate, potassium chloroplatinate, and sodium chloropalladite, which are used for sensitizing in amounts below that which produces any substantial fog inhibition, as described in Smith and Trivelli U.S. Pat. 2,448,060 issued Aug. 31, 1948, and as antifoggants in high amounts, as described in Trivelli and Smith U.S. Pats. 2,566,245 issued Aug. 28, 1951 and 2,556,263 issued Aug. 28, 1951.

The silver halide grains can also be chemically sensitized with gold salts as described in Waller et al., U.S. Pat. 2,399,083 issued Apr. 23, 1946 and Damschroder et al., U.S. Pat. 2,642,361 issued June 16, 1953. Suitable compounds are potassium chloroaurite, potassium aurithiocyanate, potassium chloroaurate, auric trichloride and 2-aurosulfobenzothiazole methochloride.

The silver halide grains can also be reduction sensitized with reducing agents, such as stannous salts (Carroll U.S. Pat. 2,487,850 issued Nov. 15, 1949), polyamines, such asdiethylene triamine (Lowe and Jones U.S. Pat. 2,518,698 issued Aug. 15, 1950), polyamines, such as spermine (Lowe and Allen U.S. Patent 2,521,925 issued Sept. 12, 1950), or bis(;3-aminoethyl)sulfide and its water-soluble salts (Lowe and Jones U.S. Patent 2,521,926, issued Sept. 12, 1950).

The silver halide grains used with this invention may be combined with speed increasing compounds such as polyalkylene glycols, cationic surface active agents and thioethers or combinations of these as described in Piper U.S. Pat. 2,886,437 issued May 12, 1959; Dann et al., U.S. Pat. 3,046,134 issued July 24, 1962; Carroll et al., U.S. Pat. 2,944,900 issued July 12, 1960; and Goffe U.S. Pat. 3,294,540 issued Dec. 27, 1966.

The stabilized silver halide grains used in the practice of this invention can be protected against the production of fog and can be further stabilized against loss of sensitivity during keeping. Suitable antifoggants and stabilizers each used alone or in combination include thiazolium salts described in Brooker et al., U.S. Pat. 2,131,- 038 issued Sept. 27, 1938 and Allen et al., U.S. Pat. 2,694,716 issued Nov. 16, 1954; the azaindenes described in Piper U.S. Pat. 2,886,437 issued May 12, 1959, and Heinbach et al., U.S. Pat. 2,444,605 issued July 6, 1948; the mercury salts as described in Allen et al. U.S. Pat. 2,728,663 issued Dec. 27, 1955; the urazoles described in Anderson et al., U.S. Pat. 3,287,135 issued Nov. 22, 1966; the sulfocatechols described in Kennard et al. U.S. Pat. 3,236,652 issued Feb. 22, 1966; the oximes described in Carroll et al. British Pat. 623,448; nitron; nitroindazoles; the mercaptotetrazoles described in Kendall et al., U.S. Pat. 2,403,927 issued July 16, 1946; Kennard et al., U.S. Pat. 3,266,897 issued Aug. 16, 1966 and Luckey et al., U.S. Pat. 3,397,987 issued Aug. 20, 1968; the polyvalent metal salts described in Jones U.S. Pat. 2,839,405 issued June 17, 1958; the thiuronium salts described in Herz et al., U.S. Pat. 3,220,839 issued Nov. 30, 1965; the palladium, platinum and gold salts described in Trivelli et al., U.S. Pat. 2,566,263 issued Aug. 28, 1951 and Yutzy et al. U.S. Pat. 2,597,915 issued May 27, 1952.

The photographic elements of this invention can contain incorporated developing agents such as hydroquinones, catechols, aminophenols 3-pyrazolidones, ascorbic acid and its derivatives, reductones and phenylenediamines. Combinations of developing agents can be employed in the practice of the invention. The developing agents can be in a silver halide emulsion and/or in another suitable location in the photographic element. The developing agents can be added from suitable solvents or in the form of dispersions as described in Yackel U.S. Pat. 2,592,368 issued Apr. 8, 1952 and Dunn et al., French Pat. 1,505,778.

The photographic and other hardenable layers used in the practice of this invention can be hardened by various organic or inorganic hardeners, alone or in combination, such as the aldehydes, and blocked aldehydes, ketones, carboxylic and carbonic acid derivatives, sulfonate esters sulfonyl halides and vinyl sulfonyl ethers, active halogen compounds, epoxy compounds, aziridines, active olefins, isocyanates, carbodiimides, mixed function hardeners and polymeric hardeners such as oxidized polysaccharides like dialdehyde starch and oxyguar gum and the like.

The photographic emulsions and elements described in the practice of this invention can contain various colloids alone or in combination as vehicles, binding agents and various layers. Suitable hydrophilic materials include both naturally-occurring substances such as proteins, for example, gelatin, gelatin derivatives, cellulose derivatives, polysaccharides such as dextran, gum arabic and the like; and synthetic polymeric substances such as water soluble polyvinyl compounds like poly(vinylpyrrolidone), acrylamide polymers and the like.

The described photographic emulsion layers and other layers of a photographic element employed in the practice of this invention can also contain alone or in cornbination with hydrophilic, water permeable colloids, other synthetic polymeric compounds such as dispersed vinyl compounds such as in latex form and particularly those which increase the dimensional stability of the photographic materials. Suitable synthetic polymers include those described, for example, in Nottorf U.S. Pat. 3,142,- 568, issued July 28, 1964; White U.S. Pat. 3,193,386, issued July 6, 1965; Houck et al., U.S. Pat. 3,062,674, issued Nov. 6, 1962; Houck et al., U.S. Pat. 3,220,844 issued Nov. 30, 1965; Ream et al., U.S. Pat. 3,287,289 issued Nov. 22, 1966; and Dykstra U.S. Pat. 3,411,911 issued Nov. 19, 1968; particularly effective are those water-insoluble polymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates, those which have cross-linking sites which facilitate hardening or curing, those having recurring sulfobetaine units as described in Dykstra Canadian Pat. 774,054.

The photographic elements used with this invention can contain antistatic or conducting layers, such layers can comprise soluble salts, e.g. chlorides, nitrates, etc., evaporated metal layers, ionic polymers such as those described in Minsk U.S. Pat. 2,861,056 issued Nov. 18, 1958 and Sterman et al., U.S. Pat. 3,206,312 issued Sept. 14, 1965 or insoluble inorganic salts such as those described in Trevoy U.S. Pat. 3,428,451 issued Feb. 18, 1969.

In addition, the photographic layers and other layers of a photographic element employed and described herein can be coated on a wide variety of supports. Typical supports include cellulose nitrate film, cellulose esterfilm, poly(vinyl acetal) film, polystyrene film, poly(ethylene terephthalate) film, polycarbonate film and related films or resinous materials, as Well as glass, paper, metal and the like. Typically, a flexible support is employed, especially a paper support, which can be partially acetylated or coated with baryta and/or an alpha-olefin polymer, particularly a polymer of an alpha-olefin containing 2 to 10 carbon atoms such as polyethylene, polypropylene, ethylenebutene copolymers and the like and on one or both sides.

The photographic layers employed in the practice of this invention can contain plasticizers and lubricants such as polyalcohols, e.g. glycerin and diols of the type described in Milton et al., U.S. Pat, 2,960,404 issued Nov. 1, 1966; fatty acids or esters such as those described in Robijns U.S. Pat. 2,588,765 issued Mar. 11, 1952 and Duane U.S. Pat. 3,121,060 issued Feb. 11, 1964; and silicone resins such as those described in DuPont British Pat. 955,061.

It is also advantageous in the practice of this invention to provide the photographic layers with surfactants such as saponin; anionic compounds such as the alkyl aryl sulfonates described in Baldsiefen U.S. Pat. 2,600,831 issued June '17, :196'2; amphoteric compounds such as those de scribed in Ben-Ezra U.S. Patent 3,133,816 issued May 19, 1964; and water soluble adducts of glycidol and an alkyl phenol such as those described in Olin Mathieson British Pat, 1,022,878.

The photographic elements employed in the practice of this invention can contain matting agents such as starch, titanium dioxide, zinc oxide, silica, polymeric beads including beads of the type described in Jelley et al., U.S. Pat. 2,992,101 issued July 11, 1961 and Lynn U.S. 'Pat. 2,701,245 issued Feb. 1, 1955.

The photographic elements used in this invention can contain brightening agents including stilbenes, triazines, oxazoles and coumarin brightening agents. Water soluble brightening agents can be used such as those described in Albers et al., German Pat. 972,067 and McFall et al., U.S. Pat. 2,933,390 issued Apr. 19, 1960 or dispersions of brighteners can be used such as those described in Jansen German Pat. 1,150,274, Oetiker et al., U.S. Pat. 3,406,070 issued Oct. 15, 1968 and Heidke French Pat. 1,530,244 and Van Campcn U.S. Pat. 3,416,923 issued Dec. 17, 1968.

The various layers, including the photographic layers, employed in the practice of this invention can contain light absorbing materials and filter dyes such as those described in Sawdey U.S. Pat. 3,252,921 issued May 31, 1966; Gaspar U.S. Pat. 2,274,782 issued Mar. 3, 1942; Silberstein et al., U.S. Pat. 2,527,583 issued Oct. 31, 1950 and Van Campen U.S. Pat. 2,956,879 issued Oct. 18, 1960. If desired, the dyes can be mordanted, for example, as described in Jones et al., U.S. Pat. 3,282,699 issued Nov. 1, 1966.

The sensitizing dyes and other addenda used in the practice of this invention can be added from water solutions or suitable organic solvent solutions can be used. The compounds can be added using various procedures including those described in Collins et al., U.S. Pat. 2,912,343 issued Nov. 10, 1959; McCrossen et al., U.S. Pat. 3,342,605 issued Sept. '19, 1967; Audran U.S. Pat. 2,996,287 issued Aug. 15, .1961 and Johnson et al., U.S. Pat. 3,425,835 issued Feb. 4, 1969.

The photographic layers used in the practice of this invention can be coated by various coating procedures including dip coating, air knife coating, curtain coating, or extrusion coating using hoppers of the type described in Beguin U.S. Pat. 2,681,294 issued June 15, 1954. If desired, two or more layers can be coated simultaneously solution of potassium bromide and potassium iodide containing 0.15 mg. of rhodium ammonium chloride/per mole of silver nitrate and a second aqueous solution of silver nitrate are simultaneously added to an aqueous gelatin solution containing the organic thioether silver halide solvent '1,8-dihydroxy-3,6-dithiaoctane at about C. with rapid stirring. A precipitate of silver bromoiodide is formed which is then washed to remove insoluble salts. This emulsion is then gold and sulfur sensitized in the conventional manner. The emulsion is stabilized by the additional 40 grams of cadmium bromide per mole of silver and 35 grams of cadmium nitrate per mole of silver. This emulsion is then coated on a polyethylene coated paper support and the element is then exposed on an intensity scale sensitometer. Processing in a conventional N-methyl-p-aminophenol sulfate-hydroquinone developer is followed by fixing, washing, and drying.

EXAMPLE II A photographic element is prepared in the same manner as in Example I except that the cadmium nitrate and cadmium bromide stabilizers are wholly replaced with only 13 grams of manganous sulfate per mole of silver. This element is then processed as described in Example I.

EXAMPLE III A third photographic element is prepared in a similar manner as described in Example I except that only 9 grams of manganous chloride per mole of silver are employed as a complete replacement for the cadmium nitrate and cadmium bromide stabilizers. Processing following exposure is accomplished as described in Example I.

The results are recorded as follows:

Resulting relative Relative Relative speed speed change on Example Stabilization addenda speed on incubation 1 incubation I Cd(NO3)2-4H2O+Cd(Br)2 +24 II. i MnSOA-HzO 118 122 +04 III l\1nCl2-4II:O 116 125 +10 1 At 50% rel. hum, 49 C. after 7 days.

by the procedures described in Russell U.S. Pat. 2,761,-

791 issued 'Sept. 4, 1956 and Wynn British Pat. 837,095. 4

In addition to the developing processes set forth in the examples, the silver halide grains and elements containing them prepared according to this invention can be processed by various methods including processing in alkaline solutions containing conventional developing agents such as hydroquinones, catechols, aminophenols, 3-pyraz0lidones, phenylenediamines, ascorbic acid derivatives, hydroxylamines, hydrazines, reductones and the like. The following examples are intended for a further understanding and description of this invention.

EXAMPLE I A silver bromoiodide emulsion (1 mole percent iodide) is prepared using the double-jet technique. An aqueous From this it is seen that the replacement of the cadmium salts by a significantly smaller concentration of manganous salts results in a marked improvement in speed stabilization represented by a significant decrease in speed change on incubation and storage. Similar results are achieved as regards stabilization of speed loss when the silver bromoiodide emulsion is prepared in the absence of the organic thioether silver halide solvent.

IEXAMPLE IV To demonstrate the unexpected nature of the results achieved with water soluble manganous salts, other metal salts are incorporated into the emulsion for comparison purposes. The procedure of Example I is followed using the metal salts listed below. The results are also listed.

1 Per mole of silver. 2 After 7 days at 49 C. and 50%relative humidity. For 7 days at 49 C. and 50% relative humidity.

9 EXAMPLE v In a manner similar to that described in Example I, another photographic emulsion is prepared containing water soluble inorganic manganous salts as a partial replacement for the cadmium salts in the control series. These results are as follows:

There is claimed:

1. A photosensitive silver halide emulsion comprising (1) silver halide grains precipitated in the presence of a rhodium salt and (2) a stabilizing concentration of (a) a water soluble manganous salt or (b) a combination of said salt with cadmium bromide.

2. The emulsion of claim 1 stabilized with said com- Concentration perm e Relative Stabilizing of silver speed, Relative Net change compounds halide, g. fresh speed 1 in speed 00 trol CdBIz 53 gggnosl-mzo a; 73 In no ven n Mnsormzo 20 97 91 --06 1 After 30 days of natural aging.

bination which comprises about to about 90 weight percent of said manganous salt.

This example clearly demonstrates that significant reductions in change of speed occur, that is, the speed is stabilized, when manganous salts are combined with significantly reduced levels of cadmium salts in the rhodium precipitated emulsions described.

Similar good results are obtained when the concentration of cadmium salts and manganous salts together are represented by as little as percent by weight of the former stabilizers. Likewise, the net change in speed on storage after incubation remains very low when the photographic elements described herein are stabilized by a combination of stabilizing addenda consisting essentially of 75 percent by weight of manganous salts and the remaining 25 percent by weight cadmium salts such as, for example, about 45 grams/mole of silver of manganous salts and about :15 grams per mole of silver of cadmium salts. Still other series confirm that similar good results are obtained when nearly equal concentrations of manganous salts and cadmium salts are used.

The results described herein are all the more unexpected in view of the significant improvement exhibited by the present high speed emulsions containing silver halide grains precipitated in the presence of rhodium in comparison to the emulsion stability exhibited by the emulsions described in Sidebotham as illustrated by Example IV. Such results are even more unexpected in view of the poor results obtained using seemingly similar compounds such as cobalt nitrate, zinc chloride and like compounds, as enumerated in Jones U.S. Pat. 2,839,405.

The invention has been described in detail wtih particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

3. The emulsion of claim 2 in which said manganous salt is manganous chloride or manganous sulfate.

4. The emulsion of claim 1 in which said concentration of said (a) water soluble manganous salt is about 3 to about 50 grams per mole of silver.

5. The emulsion of claim 2 which is a high contrast silver 'bromoiodide emulsion precipitated in the presence of said rhodium salt and an organic thioether.

6. The silver halide emulsion of claim 5, wherein said silver halide grains are precipitated in the presence of about 0.01 to about 0.25 mg. of said rhodium salt per mole of silver and about 0.1 to about 50 grams of said organic thioether per mole of silver halide.

7. A photographic element comprising a support coated with the silver halide emulsion of claim 1.

8. The element of claim 7 in which said support is paper coated with an alpha-olefin polymer.

9. A photographic element comprising a support coated with the silver halide emulsion of claim 2.

10. A photographic element comprising a support coated with the silver halide emulsion of claim 4.

11. A photographic element comprising a support coated with the silver halide emulsion of claim 5. 

